The proposed research is an integrated genetic and biochemical attack of the problem of identifying and mapping mitochondrial structural genes in Saccharomyces cerevisiae. The biological material will be a collection of petite mutants comprising overlapping deletions of the mitochondrial genome; petites with each of the known genetic markers (and many conbinations) will be obtained and characterized in terms of several genetic parameters including genotype, suppressiveness and quantitative marker transmission in crosses with wild-type tester strains. Each petite mtDNA will be characterized by restriction endonuclease analysis in order to identify which regions of the wild-type genome are present. In this way the genetic loci may by localized on specific restriction fragments and ultimately the fragments may be arranged into a physical map of wild-type. A process for assessing retained structural genes to specific restriction fragments. This process involves mating petite cells with UV-killed wild-types followed by labelling the zygotes with radioactive protein precursors; the only mitochondrial protein synthesis that can occur on such zygotes would be that using mRNA specified by the petite mtDNA that is translated on wild-type mitoribosomes. Taken as a whole it should be possible to assign specific protein gene products to the known genetic loci and to establish a detailed physical map of mtDNA. Since petites may retain as few as one structural gene, these studies should be able to identify mitochondrial gene products other than those already characterized. Additionally the proposed molecular analysis of petite mitochondrial genomes should provide new insights to the mechanism by which reiterated petite genomes arise; thus, understanding of the origin of repeated sequences, such as are found in all eucaryotic genomes, may be obtained.